The present invention relates to valve assemblies for controlling the flow of a fluid between a plurality of ports. The invention is particularly useful as a four-way change-over valve assembly in an air conditioning system, and method, for selectively operating the system according to a cooling mode or a heating mode, and is therefor described below particularly with respect to that application, but it will be appreciated that the invention and features thereof could also advantageously be used in many other applications.
Four-way change-over valves presently used in air conditioning systems have to accommodate very large pressure differentials, in the order of 30 atmospheres or more. Such high pressure differentials make it difficult to assure that the valve will not leak in its high pressure section, while at the same time to permit change-over from one operating condition to another by the use of a relatively small amount of force. Van Allen U.S. Pat. No. 2,855,000 addresses this problem in a simple manually-operated change-over valve providing only a simple change-over operation. Other four-way change-over valves hereto developed have been of a relatively complicated and expensive construction, as shown for example in U.S. Pat. Nos. 5,462,085 and 5,507,315.
Existing air-conditioning systems are also subject to a number of other problems. One problem is frosting or icing, which can occur when the system is operated in the heating mode (during the winter) or in the cooling mode (during the summer). Should frosting occur in the heating mode, the usual remedy is to change-over to the cooling mode in order to heat the outside coil, and also to shut-off the fan. As a result, considerable energy is lost, and the heating time and the heating capacity are reduced. Should frosting occur in the cooling mode, the usual remedy is to shut-off the compressor and/or to stop or change the speed of the fan, which thereby also involves a loss of energy, time, and cooling capacity. Moreover, interrupting the operation of the compressor is unhealthy to the compressor and requires waiting several minutes before its operation can be resumed. Further, to prevent frosting in the cooling mode, the system is generally designed to operate the evaporator at a temperature significantly above freezing, e.g. about 7xc2x0 C., to accommodate changes in the outside temperature; this also reduces the efficiency and cooling capacity of the system as compared, for example, when operating at a temperature closer to 0xc2x0 C.
Another problem involved in present air-conditioning systems is in reducing the cooling or heating capacity of the system, e.g. when the volume of the enclosed space to be cooled or heated is significantly reduced as by shutting off rooms, etc. The present air-conditioning systems are generally merely turned-off in order to reduce the cooling or heating capacity. However, this manner of reducing the capacity also reduces the overall efficiency of the system and wastes energy. Moreover, frequent interruption of the system tends to reduce the useful life of the compressor and the fan.
An object of the present invention is to provide an improved valve assembly which can accommodate large pressure differentials without leakage, which can be actuated from one operating condition to another by the use of a relatively small amount of force, and which can provide other controls, particularly with respect to temperature and/or output. Another object of the present invention is to an air conditioning method and system including a valve assembly which may be used not only as a normal change-over valve for changing-over the operation of the system from cooling to heating and vice versa, but which also may be used as a control valve for performing many control functions within each operational mode, including preventing frosting, defrosting, reducing system capacity when required, etc., in a more efficient manner than in the present air-conditioning systems.
According to one aspect of the present invention, there is provided a valve assembly for controlling the flow of a fluid between a plurality of ports including at least one high pressure port and one low pressure port, comprising: a base mounting the plurality of ports; and a valve member rotatable to a plurality of operational positions with respect to the base. The valve member has a control face facing the base to control the flow of fluid between the ports according to the position of the valve member with respect to the base, and an opposite face facing away from the base. The control face of the valve member is formed with a low pressure cavity in the central region thereof, and with an annular high pressure cavity in the outer region thereof completely circumscribing the low pressure cavity.
According to further features in the described preferred embodiments, the valve assembly further comprises a slow-acting vent for applying high pressure from the high pressure cavity to the opposite face of the valve member, when the valve member is in an operational position, to firmly press the valve member into sealing contact with the base, and thereby to isolate the high pressure cavity from the low pressure cavity; a pilot valve which is normally closed but selectively openable to release the high pressure applied to the opposite face of the valve member, and thereby to enable the valve member to be moved to another operational position; and a passageway from the annular high pressure section of the valve member to the opposite face of the valve member to maintain the control face of the valve member sufficiently close to the base to substantially isolate the high pressure cavity from the low pressure cavity also when the pilot valve is open and is moved to another operational position. The latter isolation is not complete because of a thin air cushion produced by the high pressure cavity between the base and valve member completely around the valve member, but is sufficient to permit the valve also to be used as a control valve to perform a number of control functions, particularly for temperature control and/or output control purposes.
As will be described below, a valve assembly constructed in accordance with the foregoing features provides a high degree of protection against leakage from its high pressure section when the valve assembly is in an operating condition, permits the valve to be changed-over to another operating condition by the application of a relatively small amount of force, and further permits the valve, to be used to perform a number of important control functions when in either operating position. The valve assembly can therefore be constructed in a simple, inexpensive and compact form, as compared to previous constructions, and is particularly useful in air-conditioning systems to be operated according to a cooling mode in the summer and a heating mode in the winter.
According to another aspect of the present invention, therefore, there is provided an air-conditioning system for air-conditioning an enclosed space by compressing and expanding a fluid, comprising: an inside heat exchanger to be located within the enclosed space; an outside heat exchanger to be located outside the enclosed space; a compressor having a low pressure side and a high pressure side; and a change-over valve. The change-over valve includes: a base having a low pressure port connected to the low pressure side of the compressor, and a high pressure port connected to the high pressure side of the compressor; a valve member rotatable with respect to the base; a rotary motor drive for driving the valve member; and a controller for controlling the rotary motor drive to selectively drive the valve member; (a) to a first position connecting the low pressure port to the inside heat exchanger and the high pressure port to the outside heat exchanger to define a low pressure section including the inside heat exchanger for using the fluid to cool the enclosed space; (b) to a second position connecting the high pressure port to the inside heat exchanger, and the low pressure port to the outside heat exchanger, to the outside heat exchanger, to the define a high pressure section including the inside heat exchanger for using the fluid to heat the enclosed space. The controller also controls the rotary motor drive for selectively driving the valve member to at least one further position, in addition to and preferably between the first and second positions. The valve member is constructed to maintain the high pressure section substantially isolated from the low pressure section, and to perform at least one additional control function, when the valve is driven to the further position.
One described additional function is to shunt a part of the fluid from the high pressure port to the low pressure port to thereby control temperature within the system without interrupting the compressor. Another described additional function is to restrict the effective cross-sectional area of the low pressure port with respect to the heat-exchanger connected to it, to thereby control the output of the system without interrupting the operation of the compressor. A further control function is to selectively open and close the pilot valve, not only for making a change-over operation, but also for controlling leakage from the high pressure port to the low pressure port for temperature control purpose in any position of the valve.
Such an air-conditioning system can therefore be operated to perform many diverse control functions, including preventing frosting or overheating, reducing system capacity, etc., in a continuous, periodic, when-required manner. This permits the air-conditioning to be designed for maximum efficiency and to be continuously controlled according to changing conditions.
According to a still further aspect of the present invention, there is provided a method of air-conditioning an enclosed space providing the advantages described above.
Further features and advantages of the invention will be apparent from the description below.